ps: error is
You have an error in your SQL syntax; check the manual that corresponds.......to use near 'serialNo = 70002B27ffawfaw' at line 1
for me it is weird, really. but I know I just can't see a very small mistake here.

I'm glad I've finally solved this problem :(
solution: I copied the DELETE FROM main..... code and then tried to execute it in the place where the problem occurs and then edit the table/variable one by one and run the program!

VB.net really doesn't care for the `````````
thing in the SQL strings.